Electrical picture transmission



Jan. 13, 1931. v E: WATSON 1,788,476

ELECTRICAL PICTURE TRANSMISSION Filed Feb. 12. 1927 2 Sheets-Sheet 1'Arromvn Patented Jan. 13,1931

UNITED STATES PATENT OFFICE EDWARD F. WATSON, OF LARCHMONT, NEW YORK,ASSIGNOR- TO AMERICAN TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATIONOF NEW YORK ELEGTRICAL PICTURE TRANSMTSSION Application fllcdlebruary12, 1927. Serial No. 167,784.

Tiii's invention relates to electro-optical transmission and moreparticularly to a p cture'transmission system in which the pleturecharacteristics are transmitted by current impulses of varying duration.

It is an object of the present inventlon to provide simple means toconvert the light effects of elemental areas of an object intoelectrical code impulses.

In the attainment of this object,'a. relay is preferably employed tocontrol the duration and character of the impulses impressed upon atransmission circuit. This relay is energize-(l by cyclicly varyingcurrent of constant amplitude which causes periodic impulses to betransmitted. This current preferably varies linearly, that is, it is ofsaw-toothed wave Form. The bias of the relay is controlled in accordancewith the tone values of the elemental areas of the picture or object atthe transmitter, thus causing corresponding variations inthe'durationsof the impulses transmitted.

The invention contemplates obtammg the cyclicly varying current byalternately charging a condenser through a resistance by currents ofopposite polarities and operating the relay as a leak on the condenser,the current through the relay being proportional to the voltage acrossthe condenser.

The invention also contemplatesobtaining the cyclicly varying waves byalternately applying voltages of opposite polarities to a series circuitcontaining inductance and re- 1 sistance and operating the relay by thecurrent through the inductance.

The arrangements for obtaining alternat ing current of saw-toothed waveform are adapted to be used in other fields than that of electricalpicture transmission. The appended claims are drafted in contemplationof such use.

A more detailed description of the invention follows and is illustratedin the accompanying drawing.

Fig. 1 is a schematic diagram of an electrical picture transmissionsystem wherein the signal forming relay is operated as a leak on thecondenser of the source of cyclic current;

Fig. 2 is a modified arrangement wherein voltages of opposite polaritiesare impressed through a resistance upon an inductance to v The operationof relay 5 which is a polar relay of well known type, is controlled bythree kinds of energizing current. A steady bias of the relay isobtained by current from battery 9 through winding 10. The amplitude ofthis biasing current is controlled by resistance 36. A cyclicallyvarying energization is obtained by current through winding 11. y A

variable bias is produced by picture current of varying amplitudeflowing through windmg 12. The combined action of these three currentscauses the armature of role. 5 to vibrate from its spacing (S) tomarking (M) contacts and vice versa at a rate determined by thefrequency of the cyclically varying current'while the periods of closureof the spacing and marking contacts are determined by the steady bias incooperation with the varying bias.

The source of cyclically varying current in Flg. 1 consists ofacondenser 13 and a resistance 14 connected in series with groundedbatteries 15 and 16 of opposite polarities through the vibratingarmature 17 of relay 18. The voltage across the condenser 13 isimpressed upon the winding 11 of relay 5 through the resistance 19. Byproperly choosing the rate of vibration of the armature 17, the voltageof batteries 15 and 16 and the constants of condenser 13 and resistances19 and 14, the current impressed upon winding 11 of relay 5 may be givena saw-toothed wave form'like that shown by graph P in Fig. 5.

ltd)

Vibrating relay 18 is a simplified form of the Gulstad vibrating relay.The simplification consists in the omission of theline winding so thatthe Operation of the relay is con trolled entirely by the constants ofthe condenser 20, resistances 21 and 22 and the inductances of theaccelerating winding 23 and the opposing'winding 24. 'For a more detailed description of the operation of this relay reference may be madeto pages 287 to 29.0 of a book by H. H. Harrison Printing TelegraphSystems and Mechanisms published by Longmans, Green and Company, NewYork, 1923.

1f the relay were energized solely by cyclically. varying current ofwave form P shown in Fig. 5, its armature would vibrate from spacing tomarking and viceversa at the same rate that the armature l? of relay 18vibrates. The durations of the spacing and marking intervals wouldtherefore be the spacing position may be completely neu-,

tralized or so nearly so that the spacing interval is of very shortduration.

The picture current flowing through winding 12 then opposes the steadybias so that the actual bias may vary from minus 100% to plus 100% Inthis specification and the accompanying drawings the convention followedwith regardto the efiect of current in the windings of relays 5 and 40is that when the voltage applied to the upper terminals is positive, thetendency is to move the armature to the marking. contact, and-when thevoltage is negative the tendency is to move the armature to the spacingcontact.

The picture current is produced in wellknown manner and is auni-directional current varying in amplitude corresponding to the tonevalues of successive elemental areas of an object or picture to betransmitted. As shown in Fig. 1 a transparency. 25 of the picture to betransmitted is mounted on a lation in the direction of the axis.

drum 26 which is adapted to be given a motion of rotation around itsaxis and of transtation of shaft 27 by a suitable source of power causesthe rotation of the drum 26 through gears 28 and 29 and the longitudinalmovement of the drum 26 by the movement of carriage 30 along the support31 by means of screw threads on the shaft'27 engaging a nut on thecarriage 30. Light from a source 32 is focused by means of lens 33 onthe surface of the transparency 25. The light passing through thetransparency The ro-v enters photoelectric cell 34 and the amount ofthis li ht is determined by the tone value of the e emental area throughwhich the light is passing. The current flowing through thephotoelectric cell is amplified preferably in an electron dischargeamplifier 35 the output current of-which flows through the winding 12 ofrelay 5. For a more detailed description of this arrangement forproducing picture currents reference may be had to Patent No. 1,654,374,Dec. 27, 1927, of J. WfHorton.

The effect of varying the bias of relay 5 is shown in; Figs. 4 'and5. Toexplain this effect let it first be assumed that relay 5 is beingenergized solely by current of sawtoothed wave form P'fiowing-in winding11. The positive half waves above the zero line 0 will then (byconvention) cause closure of the marking contact and the negative halfwaves below line 0 Will cause closure of the spacing contact. Since thepositive and negative halfzwaves are substantially equal the markingand. spacing contacts will be closed for substantially equal intervals.

Next assume that the steady biasing current I becomes effective throughwinding 10. The positive voltage from battery 9 being connected to theupper terminal of winding 10, the effect of the biasing current is totend to cause closure of the marking contact. This may be represented inFig. 5 by moving the reference line 0 to the position 0. lVith respect.to the new reference line 0' the graph P represents the combinedenergization ofirelay 5 due to the current of sawtoothedwave form P andthe steady biasing current I When this graph extends above line 0, whichfor the assumed value of L is all'the time, the marking contact of relay5 is closed. This represents the condition of plus 100% bias.

If new the picture current becomes effective in winding 12 and since theupper terminal of winding 12 has a negative voltage impressed thereon,the effect of this current is to oppose the effect of the steady biasingcurrent. The effect of this current is represented in Fig- 5 for onecondition by I and the effect on relay 5 may be represented in Fig. 5

by moving the reference line from the position 0 to the position 0 Thearmature of relay 5 willtherefore be moved to close the marking contactfor a period t during each cycle while the graph P is above thereference line 0 and to the spacing contact for a period t whilethegra'ph is below the ref erence line 0 Similarly for other values ofpicture currents represented by 1 ,1 I and L; the reference lines inFig. 5 become O 0 0 and O When the picture current has a value I thevarmature of-relay 5 will be moved to a position to closethe markingcontact for a'period tand thespacing contact for a is 2T.

5. It may be noted that for a value of picture current represented by L;the new reference line 0 coincides with the base reference line 0 forzero bias and the marking and spacin intervals are of substantiallyequal duration.

The current impulses transmitted to the line 6 for the severalconditions of Fig. 5 are shown in Fig. 4. The period of the cyclicallyvarying current is represented by 2T, therefore the interval between themidpoints of successive marking and spacing impulses is T and betweenthe mid-points of successive marking or spacing, impulses In the actualtransmission of a picture the picture current will vary from portron toportion between its maximum and minimum values and the type of impulseswhich Wlll be impressed upon line 6 is represented by the current graphof Fig. 6.

From Fig. 6 it is evident that while the time interval between themid-point of any marking or spacing interval to the mid-point of thesucceeding marking or spacing interval respectively is constant and maybe represented by 2T, the length of time between the beginning ofa'marking or a spacing interval to the beginning of the succeedingmarking or spacing interval respectively is continuously changing as thetone values of elemental areas of the picture change as shown by thedistances f, g, h, a and k.

In the foregoing description of Fig. 1 it is assumed that anincrease ofcurrent in the photoelectric cell 34 causes an increase of current inthe output circuit of the amplifier 35. Thus for a dark spot on thepicture a small amount of light passes to the photoelectric cell 34 anda small value of picture current flows in the winding 12 of relay 5.This corresponds, for example, to a value of current I in Fig. 5 andwould result in a large ratio of marking to spacing on the reproducedrecord as represented by graph A in Fig. 5, and where the ratio ofmarking to spacing is large a dark condition is represented. Obviouslythen for a light spot the picture current will be large, for example, ofthe value represented by I in Fig. 5,the ratio of marking to spacingwill be small, and the corresponding portion of the reproduced picturewill be light. Obviously by reversing the connections to the relaycontacts or reversing the action of amplifier 35 the ratio of marking tospacing can be made large for a light spot in the film and small for adark spot.

Referring now to Fig. 2 a modified arrangement is employed. Relay 40 isquite similar to relay 5 of Fig. 1 having the three energizing windings41, .42, 43. Winding 43 is the steady biasing windingwhich is energizedby current from battery 44 throu h resistance 45. finding 42 isenergized 3" picture "current from the source 46 WhlC'l may be identicalwith that shown in Fig. 1. The energizing current in winding 41 is alsoof saw-toothed wave form but this wave form is obtained in a difierentmanner, i. 0., by means of a variable resistance in series with theinductance of the relay winding.

The source of cyclically varying current in Fig. 2 consists of thewinding 41 of relay4O in series with resistance 47 upon which areimpressed positive and negative potentials from batteries 48 and 49respectively through the commutator 50 which is driven by amotor 51.

The action of the relay in impressing marking and spacing current on theline 6 is the same as in Fig. 1 which is indicated by the use of thesame reference characters.

The commutator arrangement of Fig. 2 for producing potentials ofopposite polarities in the source of cyclically varying current may beused in place of the vibrating relay of Fig. 1 and likewise thevibrating rc- 'lay of Fig. 1 may be used in place of the com mutator ofFig. 2. a

In Fig. 3 an arrangement quite similar to that of Fig. 1 is shown exceptthat winding 11 is energized by current of sine waveform obtained fromuenerator 55. In this arrangement the length of the marking and spacingimpulses are not directly proportional to the amplitude of the picturecurrent and therefore distortion would be introduced into the reproducedpicture. Under some circumstances this may not be objectionable andanimproved result may actually be obtained in improving the contrast inthe reproduced picture or other desired character istics.

A suitable type of reprodueer may be used which is operable by currentimpulses. The reproducers disclosed in Patent No. 1,613,970, Jan. 11,1927, of D. C. Tanner, are mentioned by way of example. Synchronismmust, of course, be maintained between the transmitting and reproducingdrums. Arrangements for accomplishing this result are well known in theart. I

In the arrangements selected for illustration of the inventon thespacing and marking impulses are of opposite polarity. Obviouslyimpulses of a single polarity may be I used for marking-and no currentfor spac-' ing or vice versa. The type of impulses to be used isdependent upon the nature of the transmitting channel to be employedwhich may bear-wire line, like line 6 of the drawings, either long orshort, a wire carrier'channel or a radio channel.

In order to assist in understanding the theory of the invention'and toaid in the design of actual circuits, a mathematical explanation willnow be given.

Referring to Fig. 3 the polar relay 5 is operated from a sine wave (Lsin w), the contacts of this 'rela forming the telegraph Sig-- nalsshown in Figs. 4 to 6. The reproduced picture shade can be defined aswhich will vary from 0 to 1 as the bias varies from -100% to +100%.- Therelation be tween 1 and sending picture shade S is It is seen that S andS are related by a sine function which is approximately linear over thecentral range, but will be distorted in the light and dark shades.

T his difiiculty of distortion will be over- ,g sign- (a) This will beapproximately linear for a short time and it is assumed that thecharging pe tential reverses before departing materially from linearity.The approximate equation of the straight line representing the charging5 current for the first small interval of timeis obtained by taking thefirst derivative and evaluating when t=0. That is A saw-toothed wavewillbe obtainedmhich has a slope 5? from 0 to 1r/2,'E from 1r /2 to?etc.

Let I represent the current when the reversal takes place, i. e. thepeak value of the sawtoothed wave. Then the reproduced shade and theoriginal shade are related as follows varies from 1 to l the reproducedsh'acl'e'will vary lln'early'fPGXfiO to 1 'Eqlltfl tion (5)- neglectsthe-effect of'the shunt-on the condenser and the inductance of the m layand assumes infinite sensitivity; conse* quentlyit only approximatelyrepresents actual condition.

The voltage across the condenser will riseapproxnnately l nearly-withthe time until which-forms a basis for the design of the circuitconstants. Assume that the-reversal: frequencyis 10, that is a lO-dotper second signal is to be biased from -10!) per; cent. to

+ per cent. Then v l 1 v t 0R (7) if C IOMF R- X 10 10,000. ohms.

from (4) E- 100 1 e6 oza' wl aitm That is the condenser voltage rises to1/2" of its final steady state value (with no rel eisal) in E I thesaw-toothed wave will be- 1/2 of this or 25 volts. I

Inthe circuit-ofrFig. '2, which accomplishes seconds. J The peakvalue ofthe same thing but whichdifiers inthatthe;

current through an inductance instead of voltage across acondenser 15'being; considered. The currentwave is-given by the following.-

Proceedingas before the equation of the ap-- proximate straight line isThe relation between reproduced and original shade is the same asEquation (5) namely A comparison of Equations (10) and (3) shows :thewave shapeto be identical when I L'=0R (12)" Thatis when B= 10* and L=1010- 10 =1000 henries (13),

which is probably impractical.

However; it 'is not -necessa'ry to have R as high as 10,000 ohms. forthis circuit is The design equation for a ll) cycle signal, we get riesand in Fig. 2 it would be a resistance and condenser in series. Thetheoretical equation governing their design would be the same n eachcase, namely and if R was made=R the circuit would act like a pureresistance. Practical considerations might probably prevent making R =R\Vhat is claimed is:

1. In a signaling system, a movable circuitcontrolling element, meansfor applying a linearly varying periodic force to said element toactuate it, and means 'for applying a biasing force to said elementwhich varies in accordance with signals.

2. In a signaling system, a relay, means for biasing the armature ofsaid relay, means for impressing upon said relay a linearly varyingperiodic current of constant amplitude, and means for varying the amountof bias of said armature in accordance with sig nals. i

3. In a picture transmission system, a relay. a source of "directpotential, a transmission circuit, the armature of said relaycontrolling the association of said source with said transmissioncircuit, a source of linearly varying periodic current of constantamplitude for actuatin said relay, and means for varying the bias or thearmature of said relay in accordance with the tone values of theelemental areas of the picture or object to be transmitted whereby thelength of time during which said source of direct potential isassociated with said transmitting circuit corresponds to said tonevalues.

current so as to tend to actuate it in the opposite direction. y

N5. In a picture transmission system, a source -of periodically varying"current, a source of varying current modulated in accordance'with thetone values of the elemental areas of the picture to. be transmitted, attransmitting circuit, a source of signaling voltage, and switching meansfor associating said source of signs. ing voltage with said transmittingcircuit, said switching means being actuated by said periodicallyvarying current to tend to move said switching means in one directionand by said second source of varying current to tend to movesaidswitching means in the dpposite direction.

6. In a picture transmission system, a source of alternating current, asource of pulsating current of amplitude corresponding to the tonevalues of elemental areas of a picture to be transmitted, a source ofsteady biasing current, means for producing ma netic effects by currentsfrom said sources, the

effects produced by the two last mentioned sources being in opposition,and switching means actuated by said magnetieeflt'ects' to produce codeimpulses. I

7. In a picture transmission system, a source of alternating currentWaves, having a form which rises and falls substantially linearly withtime, a relay energized by current from said source, an armature forsaid relay which vibrates under the influence of said alternatingcurrent( energization, means to produce a steady bias in said relay, asecond source of pulsating current of amplitude corresponding to thetone values of elemental areas of a picture to be transmitted, and meansto oppose the steady'bias by current from said second source forcontrolling the duration of the intervals between movements of thearmature.

"a 8. In a picture transmission system, a current operated switchingdevice, means for impressing current upon said device for caus ing aswitching operation during successive equal time intervals, means fordetermining the time of initiation of a switching operation inaccordance with the tone values of elemental areas of a picture to betransmitted, and means for producing impulses of current controlled bysaid switching device.

9. In a picture transmission system, a series circuit comprising aresistance, a condenser and a source of current, a vibrating relayhaving contacts in said series circuit adapted to change the polarity ofsaid source at uniform intervals, at multi-winding polarized relay, anenergizing circuit for one winding of said relay connected in shunt ofsaid condenser, a resistance connected in series in said energizingcircuit, a source of signaling current connected to a second winding, acontact closing armature controlled jointly by said two windings, and asignaling circuit,

ice

tea

t Qmrenti which-is controlled hysaidm mature.

.10. In a picture transmission system a series (cir u t comp i ng aresistance, arendenser and a source of current, a v brating relay havingcontacts in said series circuit ,cadapted to change the polarity of saidsource at uniform intervals, a multi-winding polarie'ed relay,anenergiaing circuit for one 0- winding of said relay connected in sh ntto -said.-condenser, a resistance connected in seniesin said energizingcircuit, a source of pic- ;ture current connected :tO a second winding,said :source comprising a photoelectric cell, 515 .an amplifier andmeans to illuminate .the photoelectric cell in accordance with the tonevalues of a-picture, -a.-contact closing armattur-econtrolled jointly bysaid :two windings {a transmission circuit the current in 120 i w ich iscontrolled by said armature.

1-1. In a picture transmission system, means :for preducing electricalcurrent'jim- -;p ulses of the same polari y d ing successive equal timeinteryfilaand means for deterininingathe time of initiation of saidimpulses gin accordance with the tone .values of elemental areas of; apicture to be trans- .mitted. I

12. {In a picturetransmission system, means forproducingelectricalcurrent impulses of the samepolari-ty duringsucoessiveequal timeintervals, and means-fordetermining both the time of'initiationand ofthe termination of said impulses in accordance with the tone 5 values ofelemental areas of ,a :picture-to be transmitted.

13. in a signaling system, aseries circuit comprising a resistance, acondenser, and a sourceof current, meansto change the polarity of saidsource at uniform intervals, a translating device having an energizingci r.

cuit connected inshunt to said condenser only,

whereby said translating device :is energized by alternating en rgyhaving .a -Wave form which rises and ialls substantially linearly withtime and means associated with said itranslatingdenice forpropagatingsignals.

' 1d. a p'icture transmission system, a

value .of the resistance and. inductance being so proportioned that thetime constant of the series circuit is appreciably greater than theinterval of time-betweenchanges of polarity of said sdurce, to producean alternating current in said inductance having a wave form which risesand falls substantially linearly with time, a movable circuitcontrolling ele-' ment, means for-applying to said element to actuateit, a linearly-Marrying periodic force produced by said alternatingcurrent, and means for applying a biasing force to said elelment whichvaries in accordance with signa- 5.

16. In a picture transmission system a series circuit comprising aresiscancejan inductance, and a source of current, means to change thepolarity of said sourceat uniform intervals. the value of the resistanceand inductance being so proportioned that the time constant of theseries circuit is appreciably greater than the interval of time betweenchanges of polarity of said source, to produce an alternating current insaid inductance having a wave form which rises and falls subsostantially linearly with time, a relay ener- I gized by said alternatingcurrent, an armature for said relay which vibrates underthe luence ofsaid alternating current waves, means !to produce-a steady bias in saidrelay, a second source of pulsatingcurrent ofarnplitude corresponding tothe tone .values of elemental areas ofa picture to be transmitted, andmeans to oppose the steady'bias by current irom said source .forcontrolling .the 1 duration of the intervals between movements of thearmature. I

In vtestimony evhereof, I have signed my name t this specification this9th day of February, 19.27..

. EDWARD F. 'WATSON.

source of alternating icurrent waves of subso .stantic ly si usoidalwere fio m, areley e eraired by current romsaidsourc'e, an arma ture forsaid relay which vibrates under the nfluence of said al ernating currentenerg cation, to produce a steadyihias in said no lian e s condsource ofpulsating current hf an'amplitud corresponding to the one alues ofelemental areas at a picture to be transknitted, an means to-opposetheste y bias Jay cur e dram said second source 2fer (coneo itrolling'thedn ticn-of the n e nalsbetwee merements .of the armature.

15.. 'In a signaling system, a series circuit comprising a resistance,an inductance, and

a-source of current, means t ohange the -po-.

5 iea'iayn fseidsaurceiatiunifiormyinterralsahe 1 DI'SQLMME1,788,476.Edward F. Watson, Larchmont, N. Y. Ennc'rmcan Pic'runn Tnims-MISSION. Patent dated 'January13, 1931. Disclaimer filed August 16,1935,

by the assignee, American Telephone and Telegraph Company.

. Hereby enters this disclaimer to the subject-matterof the said claimsof said Letters Patent which are in the following words, to wit: 4 a 14. In a signaling-system, a source of periodically varying current, asource of current varying 1n accordance with signals, a transmittingcircuit, a source of signaling transmitting circuit, said switchingmeans beingacted upo said source 'of perivoltage, switching'means forassociating said source of wag voltage with said odically varyincurrent-so as to tend to actuate it in one 'rection and by said secondsource 0 varying current so as to tend .to actuate it inthe oppositedirection. 5*. In a picture transmission system, a sourceof periodically'varymg current, a source of varying current modulated in accordancewith the tone values of the elemental areas of the picture to betransmitted, a transmitting circuit, a source of si aling voltage, andswitching means for associating said source of signaling voltage withsaid transmitting circuit, said switchingvmeans being actuated bysaicl'periodically varying current to tend to move said switching meansin one direction and by said second source of varying current to tend tomove saidswitching means in the opposite direction. I

8. In a picture transmission system, 'a current operated switchingdevice, means for impressing current upon said device for causing aswitching operation during successive equal time intervals, means fordetermining the time of initiation of a switching operation inaccordance with the tone values of elemental areas of t a picture to betransmitted, and means for producing impulses of. current controlled bysaid switchiri'gdevice. I

11. In a picture transmission system, means for producing electricalcurrent i impulses of the ,same polarity during successive equal timeintervals,- and means for determining th 'time of initiation of saidimpulses 1n accordance with the tone values of elemental areas of apicture to be transmitted.

12'. Ina picture transmission system, means for producing electricalcurrent impulses of the same polarlty during successive equal timeintervals, and means for determining both the -tiine of initiation andof the termination of said impulses 1n accordance with the tone valuesof elemental areas of a picture to be transmitted.-

[Qjfic'ial Gazette September 10, 1935.]

